This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-086386, filed Mar. 27, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a disk memory apparatus that controls the loading and unloading of a head, in accordance with the back electromotive force generated in a voice coil motor (VCM) and detected by a monitoring circuit. More particularly, the invention relates to a disk memory apparatus having the function of compensating for temperature in a circuit for monitoring the back electromotive force of a VCM, and a method for controlling of a disk memory apparatus.
Various types of disk apparatuses are known, in which a head records data on, and reproduces data from, a disk. Recently, compact magnetic disk apparatuses have been developed, in which the head is loaded and unloaded. It should be noted that the voice coil motor drives a head actuator and moves a head in a radial direction of a disk (recording media). The head remains retracted to a ramp mechanism located outside the periphery of the disk, until a read/write operation is started. When the disk is rotated to perform the read/write operation, the head is moved from the ramp (ramp mechanism) to a position above the disk. The read/write operation is then carried out under the control of a host apparatus. Shortly before stopping the rotation of the disk, the head is retracted from a position above the disk, back to the ramp.
The moving of the head from the ramp to any position above the disk is called xe2x80x9chead loading.xe2x80x9dThe moving of the head from any position above the disk to the ramp is called xe2x80x9chead unloading.xe2x80x9d
A magnetic disk apparatus of this type, in which the magnetic head is load to a position above the magnetic disk and unloaded from that position to the ramp, has a circuit for monitoring the back electromotive force generated in the voice coil motor (VCM) that drives the head. The speed of the VCM is calculated from the back electromotive force monitored by the circuit. The loading and unloading of the head is controlled in accordance with the speed of the VCM calculated.
Even if the speed of the VCM is 0, the VCM resistance changes with temperature and the amplifier gain varies. Inevitably, the output of the circuit for monitoring the back electromotive force may be proportional to the current flowing in the VCM.
Jpn. Pat. Appln. KOKAI Publication No. 11-25626 discloses a calibration technology in which a plurality of currents (VCM currents) flow through the VCM prior to the head loading. In the prior art, the offset of the circuit for monitoring back electromotive force is compensated for, in accordance with the output of the circuit.
In the prior art, the output of the monitor circuit is calibrated by passing a current in the VCM while the VCM remains retracted to the ramp mechanism before the head loading. This calibration makes it possible to properly compensate for the output of the monitor circuit in the head-loading control and to drive the VCM at an appropriate speed. A stable head loading can thereby be accomplished.
However, the temperature in the apparatus (particularly, the temperature of the VCM) at the head unloading is not always the same as the temperature at the head loading. In other words, the possibility of a temperature rising is generally high since a current keeps flowing in the VCM during the period between the head loading and the head unloading. Furthermore, the temperature in the apparatus may fall, depending on the changes in the environmental temperature. If the temperature of the VCM changes, the resistance of the VCM will change. In this case, if the output of the monitor circuit cannot be reliably corrected, the calibration value obtained during the head loading is applied to correct the output.
On the other hand, even if the calibration is executed during the head unloading in the same way as during the head loading, the unloading may not be controlled reliably. This is the reason why the head is positioned above the disk (in other words, head is not retracted to the ramp and fixed at the ramp as during the head loading). That is, if the current flows through the VCM during the head unloading, the VCM is driven and the head will move. Therefore, no reliable calibration can be accomplished as long as a current is flowing through the VCM.
Thus, if the resistance of the VCM varies due to the change of the temperature from the time of head loading to the time of head unloading, the output of the monitor circuit is calibrated incorrectly during head unloading in the same way as during the head loading. Consequently the speed of the head unloading is controlled incorrectly, the control of the speed is impossible and the control of the head unload may oscillate.
The present invention has been made in view of the foregoing. An object of the invention is to provide a disk memory apparatus having the function of compensating for temperature in a circuit for monitoring the back electromotive force of a VCM, and a method of compensating for temperature in a circuit for monitoring the back electromotive force of a VCM. In the apparatus and method, the relation between the change in temperature and the change in the calibrated output of a circuit for monitoring a back electromotive force is determined first, and the output calibrated at the head loading is corrected at the head unloading, in accordance with the temperature difference between the head loading and the head unloading.
According to an aspect of the present invention there is provided a disk memory apparatus comprising: a head configured to read or write data on or from a disk; a voice coil motor configured to move the head in a radial-direction of the disk in order to execute head-loading or head-unloading of the head; a monitor circuit configured to detect a back electromotive force generated by the voice coil motor; a first processor configured to supply a plurality of different currents to the voice coil motor at the time of the head-loading, and output a first value based on back electromotive forces each of which corresponds to the plurality of different currents and is detected the monitor circuit; a temperature sensor configured to detect a temperature of the disk memory apparatus; a second processor configured to output a second value based on a first temperature detected by the temperature sensor at the time of the head-loading and a second temperature by the temperature sensor at the time of the head-unloading, and a load/unload controller configured to control the head-loading or the head-unloading of the head in such a manner that the load/unload controller drives the voice coil motor according to the first calibration value at the time of the head-loading and drives the voice coil motor according to the second calibration value at the time of the head-unloading.
According to another aspect of the present invention there is provided a disk memory apparatus comprising: a head for reading or writing data on or from a disk; voice coil motor for moving the head in a radial-direction of the disk in order to execute head-loading or head-unloading of the head; monitor means for detecting back electromotive force generated by the voice coil motor; first calibration means for supplying a plurality of different currents to the voice coil motor at the time of the head-loading, and outputting a first value based on back electromotive forces each of which corresponds to the plurality of different currents and are detected the monitor circuit; a temperature sensor for detecting a temperature of the disk memory apparatus; second calibration means for determining a second calibration value of the monitor means on the basis of a first temperature detected by the temperature sensor at the time of the head-loading and a second temperature by the temperature sensor at the time of the head-unloading, and load/unload control means for controlling the head-loading or the head-unloading of the head in such a manner that the load/unload control means drives the voice coil motor according to the first calibration value at the time of the head-loading and drives the voice coil motor according to the second calibration value at the time of the head-unloading.
According to another aspect of the present invention there is provided a method for controlling of a disk memory apparatus comprising the steps of: supplying a plurality of different currents to voice coil motor at the time of head-loading; detecting back electromotive forces of the voice coil motor on the basis of the plurality of different currents by monitor circuit; determining a first value of the monitor circuit on the basis of the back electromotive forces; detecting a first temperature of the disk memory apparatus; controlling the voice coil motor according to the first value to execute the head-loading; detecting a second temperature of the disk memory apparatus; determining a calibration value of the monitor circuit on the basis of a first temperature and the second temperature, and controlling the voice coil motor according to the second value to execute the head-unloading.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.